Metaprogramming: The Process of Writing Code

Build Systems#

• Elements of a build system

  • dependencies
  • targets
  • rules

• Build systems avoid executing unnecessary rules for a targets whose dependencies haven't changed

• make: a common tool

  paper.pdf: paper.tex plot-data.png
      pdflatex paper.tex
  plot-%.png: %.dat plot.py
      ./plot.py -i $*.dat -o $@

  • Produce the left-hand side using the right-hand side
    • Left-hand side: target
    • Right-hand side: dependencies
    • Indented blocks: a sequence of programs to produce the target from those dependencies
    • %: the pattern to match, the requested plot-foo.png will use foo.dat

Dependency Management#

• Semantice Versioning: something like 1.3.7

  • If a release does not change the API, like fixing a security issue, increase the patch version 1.3.8
  • If you add to your API in a backwards-compatible way, increase the minor version 1.4.0
  • If you change the API in a non-backwards-compatible way, increase the major version 2.0.0

• Lock files lists the exact version you are currently depending on of each dependency

  • avoid unnecessary recompiles
  • have reproducible builds
  • not automatically update to the latest version
  • An extreme version: vendoring
    • copy all the code of your dependencies(transformers 4.1.0) into your own changes to it

Continuous Integration Systems#

• Continuous integration: "stuff that runs whenever your code changes"
  • Add a file to describe what should happen when various things happen to your repository
    • Travis CI
    • Azure Pipelines
    • Github Actions
  • The most common case: "when someone pushes code, run the test suite"
  • The class website is another example that runs the Jekyll blog software on every push to master

Testing Terminology#

• Test suite: a collective term for all the tests
• Unit test: a "micro-test" that tests a specific feature in isolation
• Integration test: a "macro-test" that runs a larger part of the system to check that different feature or components work together
• Regression test: a test that implements a particular pattern that previously caused a bug to ensure that bug does not resurface
• Mocking: to replace a function, module or type with a fake implementation to avoid testing unrelated functionality.